Talk:Benzophenone

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[edit] Benzophenone images

Hi and thanks for the benzophenone images, great!. I have some remarks on the main image though:

• how do you intent to collect the water-free toluene? I would expect you would be able to distill off the toluene once dry with a solvent still head as in [1]
• what is the purpose of the hookup to the nitrogen rack with valve open when the exit valve is closed. If you have a constant flow of inert gas during distillation there should be at least a bubble counter
• the setup is a hazard because the hookup to the water supply is not secured (the top water hose is also overstretched), the thermometer is allowed to swim in the oil bath and liable to break and the flask is not jacketed so it is not possible to do a quick cool down.

Please keep those images coming, they are great!

V8rik 17:34, 5 September 2006 (UTC)

Hi V8rik

Glad that you enjoy the pictures. I think it's quite fun that the world can see a blow-by-blow account of what I do in my lab. =)

Check out the article page. I've posted a new picture showing how I collect the dry distilled toluene. While refluxing the toluene, the stillhead, condenser, and receiving Schlenk flask are greased, fitted together, and undergo three evacuate and purge with nitrogen cycles. Of course, they are sealed as appropriate.

Once done, a positive pressure of nitrogen on the receiving assembly and the still (through the joint of the two-necked flask connected to the Schlenk line). It's a bit tricky (even with 4 hands), especially with all the water and nitrogen hoses dangling everywehre, but the main thing is to pop off both caps and fit them together quickly, while the nitrogen flow prevents air from entering. To ensure a good flow of nitrogen, the bubbler on the Schlenk line (to protect from overpressure) is turned off for a while. They are opened once the whole darn thing is assembled.

We do have something similar to http://www.sigmaaldrich.com/img/assets/4686/al_Z14785L.gif. The difference is ours is not directly connected to the receiving flask. Rather, it the sep-funnel-like bulb has another joint which is usually sealed. When we need to draw the solvent, we switch it to a septum and transfer using a cannula.

Those rigs are "standing" in that they are not set up and torn down all the time. Rather, they stir the required solvent constantly with the sodium/benzophenone, and when dry solvent is needed the heater is turned on. We don't use dry toluene that often, explaining why I had to do it separately.

Regarding the picture with the stopcock of the nitrogen line closed - nitrogen is fed from the top. There is no constant stream of nitrogen; rather, it just prevents air from leaking in. Overpressure is vented to the bubbler on the Schlenk line.

I accept your criticisms regarding the safety of the rig. There's always more for improvements. As can be seen from the mess on the benchtop, I was in a bit of a hurry when I set this up! I'm not sure what you mean about the jacketed flask, though.

--Rifleman 82 18:27, 5 September 2006 (UTC)

• Hi Rifleman 82, thanks for your reply. I guess I was just impatient, your latest image addition makes clear how the dry toluene is collected in step two. The bubble counter is there but not visible on the image, so that is cleared up as well. With jacketed I actually mean a jack [2] you can use to quickly remove the heating source from the flask but that can be regarded a matter of convenience. V8rik 22:03, 5 September 2006 (UTC)

Ah, I see. --Rifleman 82 03:02, 6 September 2006 (UTC)